Thermoplastic molding compositions based on acrylonitrile-butadiene-styrene (ABS) and a process for preparation of thermoplastic ABS molding compositions are known for years. This invention relates to special glass fiber reinforced acrylonitrile-butadiene-styrene compositions, moldings, foils, and coatings, which can be produced from thermoplastic molding compositions and glass fibers, and also to their use.
It has been known for decades that thermoplastic molding compositions can be prepared by modifying styrene-acrylonitrile copolymers via incorporation of rubbers. By way of example, this is achieved via graft copolymerization of styrene and acrylonitrile in the presence of a rubber, and also via subsequent blending of this graft copolymer with a separately prepared copolymer matrix which can, for example, be composed of a styrene-acrylonitrile copolymer or of a methylstyrene-acrylonitrile copolymer.
EP-A 0 022 200 discloses that thermoplastic molding compositions can be prepared which comprise a copolymer matrix composed of styrene and acrylonitrile, and also comprise a graft copolymer composed of a rubber latex, styrene, and acrylonitrile. Here, a polybutadiene latex is first prepared via free-radical polymerization using potassium peroxodisulfate as initiator. This rubber latex is then subjected to agglomeration, which serves to enlarge the rubber particles. This agglomeration can, for example, take place via a reaction of the rubber latex with an emulsion of a copolymer composed of ethyl acrylate and methacrylamide. The graft rubber is then prepared via reaction of the agglomerated rubber latex with styrene and acrylonitrile, using an initiator.
Glass fiber (GF) reinforced thermoplastic mixtures are also known for decades. They typically lead to an increase in rigidity and strength of the material, whereas elasticity and particularly impact strength are often significantly reduced. To achieve effective reinforcement together with a minimal loss of toughness, firm adhesion or coupling must exist between the polymer matrix and the glass fibers.
JP 56/095953 describes GF reinforced thermoplastic molding compositions containing GF-containing pellets and a GF free styrene-acrylonitrile matrix in the presence of a soluble, uncrosslinked acid containing rubber. In the process of preparation, which is difficult to control, the glass fibers are however not firmly coupled to the thermoplastic matrix.
In DE-A 33 24 909 the use of an epoxy group containing copolymer of styrene, acrylonitrile and/or methyl-methacrylate within an ABS molding composition is disclosed. Epoxy group containing copolymers however are difficult to produce in a large scale.
DE-A 34 36 602 describes GF-reinforced thermoplastic resin compounds consisting of a polymer A of styrene, acrylonitrile and methacrylates, a polymer B of styrene, acrylonitrile and maleic imides, and of polymer C containing styrene, acrylonitrile and a graft rubber D. The physical properties of the polymer mixtures show that the coupling of the glass fibers with the copolymers are inadequate.
In U.S. Pat. No. 5,039,719 the use of either maleic anhydride containing copolymers or thermoplastic polyurethanes having isocyanate groups is proposed for the use of improved coupling of glass fibers to an ABS copolymer. However, by utilizing this method, the melt flow of the resulting ABS is reduced and thus the polymer product is less suitable for injection molding.
EP-A 03 03 919 describes a glass fiber containing molding compositions of A a co-polymer of styrene and acrylnitril and B a special terpolymer of styrene, acrylonitrile and tert.-butyl(meth)acrylate, which may additionally contain a graft rubber D. The crucial monomer is tert.-butyl(meth)acrylate which decomposes at compounding temperatures above about 200° C. into (meth)acrylic acid monomer units and isobutene.
The formation of the gaseous and flammable isobutene during production however is not desirable for scaling up into an industrialized process.
U.S. Pat. No. 6,211,269 describes the utilisation of specific organic tin components to enhance the coupling reaction with GF in an ABS moulding composition. However, tin components are toxicologically adverse, especially in applications like articles for food contact, toys, cosmetic housings or medical devices.
Thus, there is the technical need to have an ABS moulding composition with improved reinforcement between the glass fibers and the copolymer, without having a negative effect on other properties such as the melt flow.